In a submarine optical transmission system, optical signals transmitted through the submarine optical fiber cable become attenuated over the length of the cable, which may stretch thousands of miles. To compensate for this signal attenuation, optical repeaters are strategically positioned along the length of the cable.
FIG. 1 illustrates a perspective view of a typical submarine optical repeater 10 having a cylindrical housing 12. A first submarine optical cable 16 enters repeater 10 at first end cover 14 and connects to first internal optical cable 18, which, in turn, connects to an optical repeater assembly 20. Optical repeater assembly 20 typically includes at least the following items (not shown in FIG. 1): optical components, connecting optical fibers, electronic circuits, and connecting wiring. Optical repeater assembly 20 connects via a second internal optical cable 19 to a second submarine optical cable 17, which exits repeater 10 at second end cover 15.
Typically, the optical fibers found within optical repeaters are circular in cross-section, and are constructed of glass surrounded by a protective jacket that is thicker than the glass. For example, a typical glass fiber ("glass fiber", "bare fiber", or "unjacketed fiber") can have an outer diameter of approximately 0.010 inches, and a typical jacketed fiber can have an outer diameter of approximately 0.040 to 0.060 inches.
The glass fiber is fragile. Because even microscopic damage to the glass fiber can adversely affect the reliability of the optical repeater (and, as a result, the reliability of the entire submarine optical fiber cable system), great efforts are normally taken to protect the glass fiber from damage. Generally, the likelihood of damage to the glass fiber can be reduced by ensuring that any curvature in the glass fiber meets or is less than the minimum bending radius of the glass fiber. However, the minimum bending radius of the glass fiber is a function of the expected life of the glass fiber. For example, when at least a 25-year life is expected, the glass fiber typically has a minimum bending radius of approximately 1 inch. This is referred to as the reliability-adjusted minimum bending radius of the glass fiber, because meeting or exceeding this value provides acceptable reliability from bending damage during the expected life of the glass fiber.
Typically, the optical components found within optical repeaters are manufacturer with a segment of optical fiber attached at each end and cut to a specified length. Each fiber segment contains a jacketed portion of specified length located adjacent to the optical component, and a bare portion of specified length extending from the opposite end of the jacketed portion. The bare portion is spliced into the bare portion of another segment in the repeater's optical circuit. Creating these splices can be a complicated task, requiring substantial lengths of bare fiber on each side of the splice. Optimally however, the repeater is designed to be as space-efficient as possible, thereby minimizing its production, storage, shipping, and installation costs. Thus, it is desirable to store each optical fiber segment in the most space-efficient manner possible.
FIG. 2 illustrates a perspective view of a known fiber storage device that can be located within, for example, a submarine optical repeater or branching unit. Tray 42 includes generally circular portal spool 44 which is surrounded by generally square portal well 48. The square portal well includes a fiber portal 68. Tray 42 also includes generally circular storage spool 46 which is surrounded by generally square storage well 50. Optical device 54 is mounted to tray 42 in optical cavity 52 which is connected to storage well 50 by cavity-to-storage channel 58 and by storage-to-cavity channel 64. Optical cavity 52 is connected to portal well 58 by portal-to-cavity channel 72 and cavity-to-portal channel 66.
Optical device 54 is connected to jacketed storage fiber 56 at the end of optical device 54 nearest storage well 50. Just inside storage well 50, jacketed storage fiber 56 connects to bare storage fiber 59. The end of bare storage fiber 59 is spliced to the end of bare connecting fiber 60 at splice 74. Bare connecting fiber 60 extends from splice 74 to jacketed connecting fiber 62 which, in turn, extends through storage-to-cavity channel 64, through optical cavity 52, through device-to-portal cavity 66, and into portal well 48. Within portal well 48, jacketed connecting fiber 62 wraps around portal spool 44 and exits at portal 68.
Jacketed connecting fiber 70 exits from the opposite end of optical device 54 and extends through portal-to-cavity channel 72, and into portal well 48, where it wraps around portal spool 44 and exits at portal 68. Spools 44 and 46 are designed with a radius greater than or equal to the reliability-adjusted minimum bending radius of the bare portion of fibers 56 and 60.
Although not shown, tray 42 can define more than one optical cavity and accompanying channels. In that situation, each additional optical fiber of any additionally mounted optical devices is routed and stored similarly to fibers 56, 59, 60, 62, and 70, i.e., in the channels connected to their respective optical cavity and around their respective spools. When more than one fiber is to be spooled around either spool 44 or 46, each additional fiber is wrapped around the spool generally above the preceding fibers, thereby forming a stack of spooled fibers.
Accessing a bare fiber stored in the known fiber storage devices can be challenging. For example, assume that four bare fibers are spooled in a stacked manner around the same spool, and that access to the bottom-most fiber in the stack is required. However, because the well is very compact, it is difficult for the assembler's fingers to reach therein, particularly when the well is more than a fraction of an inch in depth, as it typically is. Also, because the bare fibers are very small in diameter, each bare fiber can be very difficult to grab. Thus, a pointed stick is typically used to select a bare fiber and slide it to the top of well where it can be grasped. Then, the bare fiber is unspooled and moved out of the way, and the process repealed until the desired fiber is obtained. However, using a stick in this manner is a clumsy endeavor, and can cause scratches or other mechanical damage to the bare fibers. Thus, there is a need to provide an improved device for moving each spooled fiber within a fiber storage device.